Error when importing system dll

[Memnoch1207]

I am receiving this error when trying to import a system dll.

error CS0246: The type or namespace name 'sysimport' could not be found (are you missing a using directive or assembly reference?)

here is my code the line with the error is in red.

// Calling out a Win32 API function 

using System;
using System.Runtime.InteropServices;

class CH4_14
{
	[System.Runtime.InteropServices.StructLayoutAttribute
			(LayoutKind.Sequential, CharSet=CharSet.Auto)]
	public struct _SYSTEM_INFO
	{
		public int dw0emID;
		public int dwPageSize;
		public int lpMinimumApplicationAdress;
		public int lpMaximumApplicationAddress;
		public int dwActiveProcessorMask;
		public int dwNumberOfProcessors;
		public int dwProcessorType;
		public int dwAllocationGranularity;
		public short wProcessorLevel;
		public short wProcessorRevision;
	}
	
	[sysimport(dll="Kernel32.dll")]
		unsafe private static extern void
			GetSystemInfo([marshal(UnmanagedType.LPVoid)]uint* bufptr);
			
	public static unsafe void Main()
	{
		try
		{
			_SYSTEM_INFO si = new _SYSTEM_INFO();
			GetSystemInfo((uint*)&si);
			Console.WriteLine("Processor Type = {0}", si.dwProcessorType);
			Console.WriteLine("Number of Processors = {0}", si.dwNumberOfProcessors);
			Console.WriteLine("Processor Level = {0}", si.wProcessorLevel);
			Console.WriteLine("Processor Revision = {0}", si.wProcessorRevision);
		}
		
		catch(Exception e)
		{
			Console.WriteLine("Exception Caught! {0}", e);
		}
	}
}